1. Field of the Invention
The present invention relates to piezoelectric actuators, methods of manufacturing the same, ink-jet heads using the same, and ink-jet printers including such ink-jet heads and, more particularly to a piezoelectric actuator applicable to a printer contained in or connected to an electronic apparatus such as a computer, a word processor, a facsimile machine, or a copier, a method of manufacturing such a piezoelectric actuator, an ink-jet head including such a piezoelectric actuator, and an ink-jet printer including such an ink-jet head.
2. Description of the Related Art
Ink-jet heads mounted in printers are categorized into two types: a bubble-jet type and a piezoelectric type. An ink-jet head of the bubble-jet type generates air bubbles by instantaneously heating or vaporizing ink with heating elements and jetting out (spraying) the ink from nozzles by the pressure of the air bubbles. An ink-jet-head of the piezoelectric type jets out ink from nozzles by using the deformation of piezoelectric elements.
The bubble-type ink-jet head has a simple structure such that the ink-driving source (heating element) thereof can be formed by a layering process as in the case of forming a semiconductor device on a substrate. Therefore, the bubble-type ink-jet head has the advantages of high nozzle density and low cost. However, the bubble-type ink-jet head consumes a large amount of power, and has difficulty in performing fine control of ink-jet force to have the disadvantage of relatively poor print quality.
The piezoelectric-type ink-jet head, on the other hand, can perform fine control of ink-jet force so as to be capable of printing with high quality. However, compared with the bubble-type ink-jet head, the piezoelectric-type ink-jet head has a complicated structure and is inferior in terms of nozzle density and cost. Therefore, recently, a piezoelectric-type ink-jet head using a unimorph actuator formed by forming a thin film of a piezoelectric element has been proposed in order to downsize the piezoelectric-type ink-jet head and increase the nozzle density thereof.
FIG. 1 is a sectional view of an ink-jet head 10 using such unimorph actuators, showing the outline of the configuration of the ink-jet head 10. In FIG. 1, the ink-jet head 10 includes an ink supply system including ink pressure chambers 14, a pressure generation system including piezoelectric thin films 11 as piezoelectric elements generating pressure inside the ink pressure chambers 14, and nozzles 15 spraying ink particles 18 in accordance with the pressure generated inside the ink pressure chambers 14. The ink supply system is composed of a common ink channel 17 supplying ink from an ink tank (not shown in the drawing) and ink supply openings 16 connecting the common ink channel 17 to the ink pressure chambers 14.
The pressure generation system is composed of a diaphragm 13 forming one of the sidewalls of each ink pressure chamber 14, the piezoelectric thin films 11 provided thereon (thereunder in FIG. 1), and individual electrodes 12 provided on the piezoelectric thin films 11. The diaphragm 13, which is formed of, for instance, a chromium (Cr)-based conductive material, also serves as a common electrode. The diaphragm 13 is provided to cover all of the ink pressure chambers 14 provided independently along the X-axis of FIG. 1.
The piezoelectric thin films 11 and the individual electrodes 12 are provided individually for the corresponding ink pressure chambers 14. When the piezoelectric thin films 11 are supplied with electric charges between the individual electrodes 12 and the diaphragm 13, each of the piezoelectric thin films 11 deforms in proportion to the supplied amount of electric charge. The diaphragm 13 is bent as indicated by the broken line in FIG. 1 by the deformation of the piezoelectric thin films 11 so as to cause pressure inside the ink pressure chambers 14. Thereby, the ink particles 18 are jetted out from the nozzles 15 so that recording such as printing is performed on a recording medium.
As is apparent from the above description, the piezoelectric thin films 11, the individual electrodes 12, and the diaphragm 13 serve as actuators generating energy for ink ejection. If each actuator part is formed to have higher sensitivity and more durability, the performance of the ink-jet head can be improved.
Therefore, there has been proposed an ink-jet head using high-performance actuators that increase piezoelectric performance and resistance to pressure and stress by using single-crystal thin films as the piezoelectric thin films 11, thereby generating a large amount of deformation and force with a low voltage. In order to obtain the single-crystal piezoelectric thin films, however, it is required to use an expensive MgO or STO (SrTiO3) single-crystal substrate on which to form single-crystal piezoelectric thin films. Further, it is difficult to grow the MgO single crystal over a large area, thus causing the problem of an increase in the production cost.
Accordingly, it is a general object of the present invention to provide a piezoelectric actuator in which the above-described disadvantages are eliminated, a method of manufacturing such a piezoelectric actuator, an ink-jet head using such a piezoelectric actuator, and an ink-jet printer using such an ink-jet head.
A more specific object of the present invention is to provide a piezoelectric actuator including a piezoelectric thin film having high piezoelectric performance and excellent resistance to pressure and stress, a method of manufacturing such a piezoelectric actuator, an ink-jet head realizing high nozzle density and reduction in size and cost by using such a piezoelectric actuator, and an ink-jet printer using such an ink-jet head.
The above objects of the present invention are achieved by a piezoelectric actuator including a single-crystal piezoelectric thin film having a crystal orientation thereof aligned with a crystal orientation of a single-crystal Si substrate, and first and second electrode films formed on first and second sides of the single-crystal piezoelectric thin film, respectively.
The above objects of the present invention are also achieved by a piezoelectric actuator including a plurality of single-crystal piezoelectric thin films each having a crystal orientation thereof aligned with a crystal orientation of a single-crystal Si substrate, and a plurality of electrode films, wherein the single-crystal piezoelectric thin films and the electrode films are alternately layered one over another in contact with each other in a hetero-epitaxial relationship.
Compared with the conventional polycrystal piezoelectric thin film, the single-crystal piezoelectric thin film has better piezoelectric performance and resistance to pressure and stress, thus making it possible to perform finer processing on the ink-jet head.
The above objects of the present invention are also achieved by an ink-jet head including a piezoelectric actuator that includes a single-crystal piezoelectric thin film having a crystal orientation thereof aligned with a crystal orientation of a single-crystal Si substrate, and first and second electrode films formed on first and second sides of the single-crystal piezoelectric thin film, respectively.
The above objects of the present invention are also achieved by an ink-jet head including a piezoelectric actuator that includes a plurality of single-crystal piezoelectric thin films each having a crystal orientation thereof aligned with a crystal orientation of a single-crystal Si substrate, and a plurality of electrode films, wherein the single-crystal piezoelectric thin films and the electrode films are alternately layered one over another in contact with each other in a hetero-epitaxial relationship.
The piezoelectric actuators of the present invention are applied to the above-described ink-jet heads as drive sources for ejecting ink particles. Therefore, the above-described ink-jet heads realize high nozzle density, reduction in size and cost, and fine dot formation.
The above objects of the present invention are also achieved by an ink-jet printer including an ink-jet head that includes a piezoelectric actuator, the piezoelectric actuator including a single-crystal piezoelectric thin film having a crystal orientation thereof aligned with a crystal orientation of a single-crystal Si substrate, and first and second electrode films formed on first and second sides of said single-crystal piezoelectric thin film, respectively.
The above objects of the present invention are also achieved by an ink-jet printer including an ink-jet head that includes a piezoelectric actuator, the piezoelectric actuator including a plurality of single-crystal piezoelectric thin films each having a crystal orientation thereof aligned with a crystal orientation of a single-crystal Si substrate, and a plurality of electrode films, wherein the single-crystal piezoelectric thin films and the electrode films are alternately layered one over another in contact with each other in a hetero-epitaxial relationship.
The above-described ink-jet printers include the ink-jet heads of the present invention. Therefore, the above-described ink-jet printers are reduced in size and provide high image quality.
The above objects of the present invention are further achieved by a method of manufacturing a piezoelectric actuator, the method including the steps of (a) preparing a single-crystal Si substrate, growing an intermediate film hetero-epitaxially on a surface of the single-crystal Si substrate, and growing a piezoelectric thin film hetero-epitaxially on the intermediate film, and (b) removing part of the single-crystal Si substrate, the part corresponding to a region driven by the piezoelectric thin film.
The piezoelectric actuators of the present invention are manufactured by the above-described method.